Nuclear plates have been used as a means of recording track of charged elementary particles in cosmic rays or in nuclear reaction, to make analytical researches in their characteristics (Kagaku Shashin Binran (Science Photography Handbook), Vol. I, Paragraph 11.4; Vol. II, Paragraph 4.1 (Maruzen); and Butsurigaku Sensho 7 Hoshasen Keisokugaku (Physics selection 7 Radiation Metrology), Chapter 6, Paragraph 3 (Shoukabo Gomei Kaisha)).
Generally, a nuclear plate comprises a coated silver halide emulsion, of tens of μm to hundreds of μm thickness, in high density on one or both surfaces of a transparent support, such as a glass plate and a plastic film.
In the nuclear plate, charged elementary particles that pass through silver halide crystals of a silver halide emulsion, give energy to the silver halide crystals, and as a result, latent images are formed in the crystals due to the electrons generated on the ionization. As to the charged particles, such as electron rays and α-rays, latent images are formed in the silver halide grains in accordance with tracks of charged particles. On the other hand, as to γ-rays and X-rays, latent images are not directly formed in accordance with tracks of these rays, but with tracks of electrons generated by photoelectric effect, Compton effect, or the like.
The nuclear plate having a latent image formed is processed to visualize the image as black silver. The visualized black silver grains are investigated by means of an optical microscope, to detect tracks of the particles, thereby identifying kinds and properties of the charged particles.
The nuclear plate that can directly capture π meson, muon, τ-particles, Charm particles, and the like, remarkably contributed to the progress of elementary particle physics.
The silver halide emulsion for a nuclear plate that is to be used as mentioned above is required to exhibit a photographic property that is high in the number of developed silver grains formed per unit length of track, while considerably low in fog. Generally, the number of developed silver grains referred to as Grain Density (=GD) and means the number of developed silver per 100 μm of a track that an electron-ray of a minimum ionizing particle forms. Fog is represented by the number of fogged grains per 1000 μm3 and is referred to as Fog Density (=FD). For the above-mentioned purpose, generally, use has been made of emulsions in which silver bromide or silver iodobromide particulate crystals, of uniform size, are densely dispersed in a gelatin binder.
In the nuclear plate, latent images are accumulatively formed upon exposure to natural radiation and cosmic rays in the period of time between coating of a silver halide emulsion on a support and use of the coated silver halide emulsion for investigation. The resulting latent images inevitably form tracks that become harmful noises in a track analysis for a target charged particle of interest. Accordingly, to make the influence of undesired exposure as small as possible, there has been employed a method in which a researcher coats a silver halide emulsion, in a laboratory, just before starting experimentation, and then uses the obtained plate. However, this method is not satisfactory because of such disadvantages that much labor is required and uniform coating is difficult.
In view of the above, there has been developed, for example, a method in which a treatment called refresh treatment (forced fading treatment) is carried out before use. The refresh treatment is to eliminate latent images formed by cosmic rays and accumulated in the coated dry plate before starting experimentation (elimination of Background-Track).
However, previous silver halide emulsions provided for the nuclear plate have such disadvantages as that, by a fading treatment, a latent image is not sufficiently eliminated, fog is increased, or, even though a latent image is sufficiently eliminated, the objective sensitivity after the treatment decreases. Accordingly, there is strong demand for a nuclear plate that is excellent in fading treatment suitability.
Further, previous nuclear plates have such problems as that, in the case of handling a lot of nuclear plates, abrasion marks (fog) easily increase, and dry plates easily adhere with each other, and also, in the case of a glass plate, the dry plate is heavy and breaks easily.
Besides, previous nuclear plates may be processed using a methol/hydroquinone series developer, which is used in a processing of black and white photographic light-sensitive material. However, in the case of processing a nuclear plate coated with a thick emulsion layer, the general method is to use amidol as a developing agent, and conduct development at a low pH and a low temperature for a long time (see Kagaku Shashin Binran (Science Photography Handbook), Vol. II, Paragraph 4.1, pp. 140 to 141 (Maruzen); Butsurigaku Sensho 7 Hoshasen Keisokugaku, Chapter 6, Paragraph 3, pp. 182 to 183 (Shoukabo Gomei Kaisha); and the like).
However, because of a disadvantage that the amidol-developing agent, which is readily oxidized, requires preparation of a developer just before use, there is needs for development of a new processing solution for nuclear plates that is excellent in both stability and handling properties, and suitable for processing a lot of dry plates.